1. Technical Field
The present invention relates to an image processing apparatus which quantizes a pixel value of each of a plurality of pixels contained in an input image, based on a quantization threshold, performs a diffusion process of diffusing a quantization error generated by quantization to neighborhood pixels of each pixel, and generates an output image of halftone, an image forming apparatus provided with said image processing apparatus, a recording medium recording a computer program for realizing said image processing apparatus, and an image processing method.
2. Description of Related Art
In recent years, digitization of office automation equipments progresses rapidly, and demand of color image output increases, thereby an output device, such as a digital color copying machine of an electrophotographying system, a color printer of an inkjet system or a heat transfer system prevails widely. For example, an image inputted from an input device such as a digital camera or an image scanner, or an image created by a computer is outputted using such an output device. Generally, since the number of gray scales of an image which can be outputted by such an output device is fewer than the number of gray scales of an input image to be inputted from the input device, it is often the case that a pseudo-tone reproduction process is performed with respect to the input image.
There is an error diffusion process as one technique of the pseudo-tone reproduction process. The error diffusion process is a pseudo-halftone process of generating an output image reproduced with pseudo-halftone by lowering a gray scale of an input image, while maintaining the characteristic of the input image having a shade part. Moreover, an image processing method is proposed such that optimal output images are obtained with respect to input images of various conditions.
For example, the following image processing method is disclosed. In the method, a setting circuit is provided which sets up an error diffusion parameter according to at least one data of area data extracted from an inputted tone image, zoom level data, and average density data of pixels, and in the case of a reduction process, an error diffusion parameter for lowering density in a reproduction image is set up, and in the case of an enlargement process, a threshold and a limiter are adjusted so that an error may not occur as much as possible, or an error diffusion parameter is set up such that a simple binarization is performed without diffusing an error, thereby obtaining a reproduction image with high quality (refer to Japanese Patent Application Laid-Open No. H9-247447 (1997)).